Interpretive Summary: Dairy proteins can be used to boost the protein content in puffed snacks made from corn meal, but they bind water and form doughy pastes with starch. To reduce the water binding property of dairy proteins, whey protein isolate (WPI), or whey protein concentrates (WPC), or nonfat dried milk (NDM) - concentrated forms of whey – were modified using an extruder. The extruder is a machine with two mixing screws inside a long heated barrel used to make puffed snacks. The extruder temperature conditions were adjusted to 50, 75, or 100 degrees C, sufficient to change the structure of the dairy proteins, but not destroy them. Running the dairy proteins through the extruder modified their structures, making them less doughy and easier to use in starchy foods for boosting nutrient levels. For example, modified whey protein is more compatible with corn meal and forms better puffed snacks. This knowledge would allow the creation of nutritious extruded foods that uses whey protein, a byproduct of the cheesemaking process.

Technical Abstract:
Dairy proteins are amenable to structural modifications induced by high temperature, shear and moisture; in particular, whey proteins can change conformation to new unfolded states. The change in protein state is a basis for creating new foods. The dairy products, nonfat dried milk (NDM), whey protein concentrate (WPC), and whey protein isolate (WPI) were modified using a twin-screw extruder at melt temperatures of 50, 75, and 100 degrees C, and moistures ranging from 20 to 70 wt%. Viscoelasticity and solubility measurements showed that extrusion temperature was a more significant (p<0.05) change factor than moisture content. The degree of texturization, or change in protein state, was characterized by solubility (R2=0.98). The consistency of the extruded dairy protein ranged from rigid (2500 N) to soft (2.7 N). Extruding at or above 75 degrees C resulted in increased peak force for WPC (138 to 2500 N) and WPI (2.7 to 147.1 N). NDM was marginally texturized; the presence of lactose interfered with its texturization. WPI products extruded at 50 degrees C were not texturized; their solubility values ranged from 71.8 to 92.6%. A wide possibility exists for creating new foods with texturized dairy proteins due to the extensive range of states achievable.